Mill guide and anchor assembly for subterranean well casings

Abstract

A retrievable mill guide and anchor assembly is provided for use in forming a side wall window in a vertical subterranean well casing for subsequent connection to the casing of a lateral bore liner member extending through the casing window. The mill guide extends upwardly from the top end or the anchor. With the assembly in its run-in orientation, a milling pipe with a first mill bit on its lower end is releasably locked within the upper mill guide end, and pressurized fluid within the milling pipe is used to hydraulically set the anchor in the casing. After the anchor is set, the first mill bit is rotated, lowered and deflected by the mill guide to engage and form an initial opening in the casing side wall. The milling pipe is then removed from the casing, the first mill bit is replaced with a second mill bit, and a specially designed retrieval collet is installed on the milling pipe. The milling pipe is then lowered into the casing, and the second mill bit is used in conjunction with the mill guide to enlarge the casing side wall opening to the final desired window size. The retrieval collet is then latched into the upper mill guide end and pulled up to sequentially release the anchor and pull the mill guide and anchor assembly out of the casing with the milling pipe.